What is the meaning of dumb?

adjective

• Slow to learn or understand; lacking intellectual acuity.
  • usage: "so dense he never understands anything I say to him"; "never met anyone quite so dim"; "although dull at classical learning, at mathematics he was uncommonly quick- Thackeray; "dumb officials make some really dumb decisions"; "he was either normally stupid or being deliberately obtuse"; "worked with the slow students"
  • synonyms: dense, dim, dull, obtuse, slow
• Temporarily incapable of speaking.
  • usage: "struck dumb"; "speechless with shock"
  • synonyms: speechless
• Lacking the power of human speech.
  • usage: "dumb animals"
• Unable to speak because of hereditary deafness.
  • synonyms: mute, silent